/*
 * Arcfour (RC4) implementation for PuTTY.
 *
 * Coded from Schneier.
 */

#include <assert.h>
#include "ssh.h"

typedef struct
{
    unsigned char i, j, s[256];
} ArcfourContext;

static void arcfour_block(void *handle, unsigned char *blk, int len)
{
    ArcfourContext *ctx = (ArcfourContext *) handle;
    unsigned k;
    unsigned char tmp, i, j, *s;

    s = ctx->s;
    i = ctx->i;
    j = ctx->j;
    for (k = 0; (int) k < len; k++)
    {
        i = (i + 1) & 0xff;
        j = (j + s[i]) & 0xff;
        tmp = s[i];
        s[i] = s[j];
        s[j] = tmp;
        blk[k] ^= s[(s[i] + s[j]) & 0xff];
    }
    ctx->i = i;
    ctx->j = j;
}

static void arcfour_setkey(ArcfourContext *ctx, unsigned char const *key,
                           unsigned keybytes)
{
    unsigned char tmp, k[256], *s;
    unsigned i, j;

    s = ctx->s;
    assert(keybytes <= 256);
    ctx->i = ctx->j = 0;
    for (i = 0; i < 256; i++)
    {
        s[i] = i;
        k[i] = key[i % keybytes];
    }
    j = 0;
    for (i = 0; i < 256; i++)
    {
        j = (j + s[i] + k[i]) & 0xff;
        tmp = s[i];
        s[i] = s[j];
        s[j] = tmp;
    }
}

/* -- Interface with PuTTY -- */

/*
 * We don't implement Arcfour in SSH-1 because it's utterly insecure in
 * several ways.  See CERT Vulnerability Notes VU#25309, VU#665372,
 * and VU#565052.
 *
 * We don't implement the "arcfour" algorithm in SSH-2 because it doesn't
 * stir the cipher state before emitting keystream, and hence is likely
 * to leak data about the key.
 */

static void *arcfour_make_context(void)
{
    return snew(ArcfourContext);
}

static void arcfour_free_context(void *handle)
{
    sfree(handle);
}

static void arcfour_stir(ArcfourContext *ctx)
{
    unsigned char *junk = snewn(1536, unsigned char);
    memset(junk, 0, 1536);
    arcfour_block(ctx, junk, 1536);
    memset(junk, 0, 1536);
    sfree(junk);
}

static void arcfour128_key(void *handle, unsigned char *key)
{
    ArcfourContext *ctx = (ArcfourContext *) handle;
    arcfour_setkey(ctx, key, 16);
    arcfour_stir(ctx);
}

static void arcfour256_key(void *handle, unsigned char *key)
{
    ArcfourContext *ctx = (ArcfourContext *) handle;
    arcfour_setkey(ctx, key, 32);
    arcfour_stir(ctx);
}

static void arcfour_iv(void *handle, unsigned char *key)
{

}

const struct ssh2_cipher ssh_arcfour128_ssh2 = { arcfour_make_context,
          arcfour_free_context, arcfour_iv, arcfour128_key, arcfour_block,
          arcfour_block, "arcfour128", 1, 128, 0, "Arcfour-128"
      };

const struct ssh2_cipher ssh_arcfour256_ssh2 = { arcfour_make_context,
          arcfour_free_context, arcfour_iv, arcfour256_key, arcfour_block,
          arcfour_block, "arcfour256", 1, 256, 0, "Arcfour-256"
      };

static const struct ssh2_cipher *const arcfour_list[] = { &ssh_arcfour256_ssh2,
           &ssh_arcfour128_ssh2,
       };

const struct ssh2_ciphers ssh2_arcfour = { sizeof(arcfour_list)
    / sizeof(*arcfour_list), arcfour_list
};
